Never disconnect any charging unit circuit or battery
circuit cable from battery when the charging unit is
operated. A spark can cause an explosion from the
flammable vapor mixture of hydrogen and oxygen that is
released from the electrolyte through the battery outlets.
Injury to personnel can be the result.
The battery circuit is an electrical load on the charging unit.
The load is variable because of the condition of the charge in
the battery. Damage to the charging unit will result if the
connections (either positive or negative) between the battery
and charging unit are broken while the charging unit is in
operation. This is because the battery load is lost and there is
an increase in charging voltage. High voltage will damage, not
only the charging unit, but also the regulator and other
Use the 4C4911 Battery Load Tester, the 8T0900 Clamp-On
Ammeter and the 6V7070 Multimeter to load test a battery that
does not hold a charge when in use. See Special Instruction,
SEHS7633 for the correct procedure and specifications to use.
The condition of charge in the battery at each regular
inspection will show if the charging system operates correctly.
An adjustment is necessary when the battery is constantly in a
low condition of charge or a large amount of water is needed
(more than one ounce of water per cell per week or per every
100 service hours).
When it is possible, make a test of the charging unit and
voltage regulator on the engine, and use wiring and
components that are a permanent part a the system. Off-
engine (bench) testing will give a test of the charging unit and
voltage regulator operation. This testing will give an indication
of needed repair. After repairs are made, again make a test to
give proof that the units are repaired to their original condition
Before the start of on-engine testing, the charging system and
battery must be checked as shown in the Steps that follow:
Battery must be at least 75 percent (1.225 Sp.Gr.) fully
charged and held tightly in place. The battery holder
must not put too much stress on the battery.
Cables between the battery, starter and engine ground
must be the correct size. Wires and cables must be free
of corrosion and have cable support clamps to prevent
stress on battery connections (terminals).
Leads, junctions, switches and panel instruments that
have direct relation to the charging circuit must give
correct circuit control.
Inspect the drive components for the charging unit to be
sure they are free of grease and oil and have the ability
to operate the charging unit.
Make reference to the Specifications section of the complete
service manual to find all testing specifications for the
alternators and regulators.
No adjustment can be made to change the rate of charge on
24V alternator regulators. If rate of charge is not correct, a
replacement of the alternator regulator is necessary.
Heavy-Duty Digital Multimeter
Use a DC Voltmeter to find starting system components which
do not function.
Move the start control switch to activate the starter solenoid.
Starter solenoid operation can be heard as the pinion of the
starter motor is engaged with the ring gear on the engine
If the solenoid for the starter motor will not operate, it is
possible that the current from the battery did not get to the
solenoid. Fasten one lead of the voltmeter to the connection
(terminal) for the battery cable on the solenoid. Put the other
lead to a good ground. No voltmeter reading shows there is
broken circuit from the battery. More testing is necessary
when there is a reading on the voltmeter.